Never Mind I have find the solution on this thread.
In case anyone needs it :
add_shortcode( 'cus_wishlist_shortcode', 'woo_wishlist_shortcode_func' );
function woo_wishlist_shortcode_func() {
if ( ! is_object( $product) ) {
$product = wc_get_product( get_the_ID() );
$wt_wishlist = new WT_Wishlist_Singlepage();
$wt_wishlist->render_webtoffee_wishlist_button();
}
}